On Wed, Aug 18, 2004 at 02:29:57PM -0400, Peter C. Lai said: > On Wed, Aug 18, 2004 at 09:08:12PM +0300, Claudiu wrote: > > hello, > > > > please explain what do you mean by "reverse the hash". Is this the > > recreation of the originial message from its hash ? > > The short answer is yes. The slightly longer answer is that such is only one > specific case. The general case is that the digest should not reveal any > information about the original message. well, technically you're not "reversing the hash": you can't re-create a message from its hash, because the information is simply gone--digesting algorithms are massively lossy by definition. that is, you can't take a 128-bit MD5 hash and recover the original 2-megabyte message, which makes sense. what you can do, if you have a proper attack formula, is find *a* message that produces *that one hash*. that is, if I have message M which produces hash H, I can use the attack to find *a* message M' which will also produce hash H. I suppose the possibility exists that M' will equal the original M, but I'd speculate that the odds are remarkably small. chris ------------------------------- Chris Doherty chris [at] randomcamel.net "I think," said Christopher Robin, "that we ought to eat all our provisions now, so we won't have so much to carry." -- A. A. Milne ------------------------------- _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-security To unsubscribe, send any mail to "[email protected]"